Cellular membranes represent a large store of second messengers that can be enlisted in a variety of signal transduction pathways. In relation to function and regulation of effector enzymes in phospholipids signalling pathways, class I PI3-kinases (e.g. PI3Kdelta) generate second messengers from the membrane phospholipid pools. Class I PI3Ks convert the membrane phospholipid PI(4,5)P2 into PI(3,4,5)P3, which functions as a second messenger. PI and PI(4)P are also substrates of PI3K and can be phosphorylated and converted into PI3P and PI(3,4)P2, respectively. In addition, these phosphoinositides can be converted into other phosphoinositides by 5′-specific and 3′-specific phosphatases. Thus, PI3K enzymatic activity results either directly or indirectly in the generation of two 3′-phosphoinositide subtypes which function as second messengers in intracellular signal transduction pathways (Trends Biochem. Sci. 22(7) p. 267-72 (1997) by Vanhaesebroeck et al.; Chem. Rev. 101(8) p. 2365-80 (2001) by Leslie et al.; Annu. Rev. Cell Dev. Biol. 17 p. 615-75 (2001) by Katso et al.; and Cell. Mol. Life Sci. 59(5) p. 761-79 (2002) by Toker). To date, eight mammalian PI3Ks have been identified, divided into three main classes (I, II, and III) on the basis of sequence homology, structure, binding partners, mode of activation, and substrate preference. In vitro, class I PI3Ks can phosphorylate phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PI4P), and phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) to produce phosphatidylinositol-3-phosphate (PI3P), phosphatidylinositol-3,4-bisphosphate (PI(3,4)P2, and phosphatidylinositol-3,4,5-trisphosphate (PI(3,4,5)P3, respectively. Class II PI3Ks can phosphorylate PI and PI4P. Class III PI3Ks can only phosphorylate PI (Vanhaesebroeck et al. (1997), above; Vanhaesebroeck et al. Exp. Cell Res. 253(1) p. 239-54 (1999); and Leslie et al. (2001), above).
Class I PI3K is a heterodimer consisting of a p110 catalytic subunit and a regulatory subunit, and the family is further divided into class Ia and class Ib enzymes on the basis of regulatory partners and mechanism of regulation. Class Ia enzymes consist of three distinct catalytic subunits (p110α, p110β, and p110δ) that dimerise with five distinct regulatory subunits (p85α, p55α, p50α, p85β, and p55γ), with all catalytic subunits being able to interact with all regulatory subunits to form a variety of heterodimers. Class Ia PI3K are generally activated in response to growth factor-stimulation of receptor tyrosine kinases, via interaction of the regulatory subunit SH2 domains with specific phospho-tyrosine residues of the activated receptor or adaptor proteins such as IRS-1. Small GTPases (ras as an example) are also involved in the activation of PI3K in conjunction with receptor tyrosine kinase activation. Both p110α and p110β are constitutively expressed in all cell types, whereas p110δ expression is more restricted to leukocyte populations and some epithelial cells. In contrast, the single Class Ib enzyme consists of a p110γ catalytic subunit that interacts with a p101 regulatory subunit. Furthermore, the Class Ib enzyme is activated in response to G-protein coupled receptor (GPCR) systems and its expression appears to be limited to leukocytes.

As illustrated in Scheme A above, phosphoinositide 3-kinases (PI3Ks) phosphorylate the hydroxyl of the third carbon of the inositol ring. The phosphorylation of phosphoinositides to generate PtdIns(3,4,5)P3, PtdIns(3,4)P2 and PtdIns(3)P, produces second messengers for a variety of signal transduction pathways, including those essential to cell proliferation, cell differentiation, cell growth, cell size, cell survival, apoptosis, adhesion, cell motility, cell migration, chemotaxis, invasion, cytoskeletal rearrangement, cell shape changes, vesicle trafficking and metabolic pathway (Katso et al. (2001), above; and Mol. Med. Today 6(9) p. 347-57 (2000) by Stein et al.).
The activity of PI3-kinases responsible for generating these phosphorylated signalling products was originally identified as being associated with viral oncoproteins and growth factor receptor tyrosine kinases that phosphorylate phosphatidylinositol (PI) and its phosphorylated derivatives at the 3′-hydroxyl of the inositol ring (Panayotou et al. Trends Cell Biol. 2 p. 358-60 (1992)). However, more recent biochemical studies have revealed that class I PI3-kinases (e.g. class IA isoform PI3Kδ) are dual-specific kinase enzymes, meaning they display both lipid kinase (phosphorylation of phosphoinositides) as well as protein kinase activity, which have been shown to be capable of phosphorylation of other protein as substrates, including auto-phosphorylation as an intramolecular regulatory mechanism (EMBO J. 18(5) p. 1292-302 (1999) by Vanhaesebroeck et al.). Cellular processes in which PI3Ks play an essential role include suppression of apoptosis, reorganization of the actin skeleton, cardiac myocyte growth, glycogen synthase stimulation by insulin, TNFα-mediated neutrophil priming and superoxide generation, and leukocyte migration and adhesion to endothelial cells.
PI3-kinase activation, is believed to be involved in a wide range of cellular responses including cell growth, differentiation, and apoptosis (Parker, Current Biology 5(6) p. 577-79 (1995); and Yao et al. Science 267(5206) p. 2003-06 (1995)). PI3-kinase appears to be involved in a number of aspects of leukocyte activation. A p85-associated PI3-kinase has been shown to physically associate with the cytoplasmic domain of CD28, which is an important costimulatory molecule for the activation of T-cells in response to antigen (Pàges et al. Nature 369 p. 327-29 (1994); and Rudd, Immunity 4 p. 527-34 (1996)). Activation of T cells through CD28 lowers the threshold for activation by antigen and increases the magnitude and duration of the proliferative response. These effects are linked to increases in the transcription of a number of genes including interleukin-2 (IL2), an important T cell growth factor (Fraser et al. Science 251(4991) p. 313-16 (1991)).
PI3Kγ has been identified as a mediator of G beta-gamma-dependent regulation of JNK activity, and G beta-gamma are subunits of heterotrimeric G proteins (Lopez-Ilasaca et al. J. Biol. Chem. 273(5) p. 2505-8 (1998)). Recently, (Laffargue et al. Immunity 16(3) p. 441-51 (2002)) it has been described that PI3Kγ relays inflammatory signals through various G(i)-coupled receptors and is central to mast cell function, stimuli in the context of leukocytes, and immunology including cytokines, chemokines, adenosines, antibodies, integrins, aggregation factors, growth factors, viruses or hormones for example (J. Cell Sci. 114 (Pt 16) p. 2903-10 (2001) by Lawlor et al.; Laffargue et al. (2002), above; and Curr. Opinion Cell Biol. 14(2) p. 203-13 (2002) by Stephens et al.).
Specific inhibitors against individual members of a family of enzymes provide invaluable tools for deciphering functions of each enzyme. Two compounds, LY294002 and wortmannin (hereinafter), have been widely used as PI3-kinase inhibitors. These compounds are non-specific PI3K inhibitors, as they do not distinguish among the four members of Class I PI3-kinases. For example, the IC50 values of wortmannin against each of the various Class I PI3-kinases are in the range of 1-10 nM. Similarly, the IC50 values for LY294002 against each of these PI3-kinases is about 15-20 μM (Fruman et al. Ann. Rev. Biochem. 67 p. 481-507 (1998)), also 5-10 microM on CK2 protein kinase and some inhibitory activity on phospholipases. Wortmannin is a fungal metabolite which irreversibly inhibits PI3K activity by binding covalently to the catalytic domain of this enzyme. Inhibition of PI3K activity by wortmannin eliminates subsequent cellular response to the extracellular factor. For example, neutrophils respond to the chemokine fMet-Leu-Phe (fMLP) by stimulating PI3K and synthesizing PtdIns (3, 4, 5)P3. This synthesis correlates with activation of the respiratory burst involved in neutrophil destruction of invading microorganisms. Treatment of neutrophils with wortmannin prevents the fMLP-induced respiratory burst response (Thelen et al. Proc. Natl. Acad. Sci. USA 91 p. 4960-64 (1994)). Indeed, these experiments with wortmannin, as well as other experimental evidence, show that PI3K activity in cells of hematopoietic lineage, particularly neutrophils, monocytes, and other types of leukocytes, is involved in many of the non-memory immune response associated with acute and chronic inflammation.

Based on studies using wortmannin, there is evidence that PI3-kinase function is also required for some aspects of leukocyte signaling through G-protein coupled receptors (Thelen et al. (1994), above). Moreover, it has been shown that wortmannin and LY294002 block neutrophil migration and superoxide release.
It is now well understood that deregulation of oncogenes and tumour suppressor genes contributes to the formation of malignant tumours, for example by way of increased cell growth and proliferation or increased cell survival. It is also now known that signalling pathways mediated by the PI3K family have a central role in a number of cell processes including proliferation and survival, and deregulation of these pathways is a causative factor a wide spectrum of human cancers and other diseases (Katso et al. Annual Rev. Cell Dev. Biol. (2001) 17 p. 615-675 and Foster et al. J. Cell Science (2003) 116(15) p. 3037-3040). PI3K effector proteins initiate signalling pathways and networks by translocating to the plasma membrane through a conserved Pleckstrin Homology (PH) domain, which specifically interacts with PtdIns(3,4,5)P3 (Vanhaesebroeck et al. Annu. Rev. Biochem. (2001) 70 p. 535-602). The effector proteins signalling through PtdIns(3,4,5)P3 and PH domains include Serine/Threonine (Ser/Thr) kinases, Tyrosine kinases, Rac or Arf GEFs (Guanine nucleotide exchange factors) and Arf GAPs (GTPase activating proteins).
In B and T cells PI3Ks have an important role through activation of the Tec family of protein tyrosine kinases which include Bruton's tyrosine kinase (BTK) in B cells and Interleukin-2-inducible T-cell kinase (ITK) in T cells. Upon PI3K activation, BTK or ITK translocate to the plasma membrane where they are subsequently phosphorylated by Src kinases. One of the major targets of activated ITK is phospholipase C-gamma (PLCγ1), which hydrolyses PtdIns(4,5)P2 into Ins(3,4,5)P3 and initiates an intracellular increase in calcium levels and diacylglycerol (DAG) which can activate Protein Kinases C in activated T cells.
Unlike the Class IA p110α and p110β, p110δ is expressed in a tissue restricted fashion. Its high expression level in lymphocytes and lymphoid tissues suggests a role in PI3K-mediated signalling in the immune system. The p110δ kinase dead knock-in mice are also viable and their phenotype is restricted to defects in immune signalling (Okkenhaug et al. Science (2002) 297 p. 1031-4). These transgenic mice have offered insight into the function of PI3Kδ in B-cell and T-cell signalling. In particular, p110δ is required for PtdIns(3,4,5)P3 formation downstream of CD28 and/or T cell Receptor (TCR) signalling. A key effect of PI3K signalling downstream of TCR is the activation of Akt, which phosphorylates anti-apoptotic factors as well as various transcription factors for cytokine production. As a consequence, T cells with inactive p110δ have defects in proliferation and Th1 and Th2 cytokine secretion. Activation of T cells through CD28 lowers the threshold for TCR activation by antigen and increases the magnitude and duration of the proliferative response. These effects are mediated by the PI3Kδ-dependent increase in the transcription of a number of genes including IL2, an important T cell growth factor.
Therefore, PI3K inhibitors are anticipated to provide therapeutic benefit via its role in modulating T-cell mediated inflammatory responses associated to respiratory diseases such as asthma, COPD and cystic fibrosis. In addition, there is indication that T-cell directed therapies may provide corticosteroid sparing properties (Alexander et al. Lancet (1992) 339 p. 324-8) suggesting that it may provide a useful therapy either as a standalone or in combination with inhaled or oral glucocorticosteroids in respiratory diseases. A PI3K inhibitor might also be used alongside other conventional therapies such as a long acting beta-agonist (LABA) or leukotriene antagonist in asthma.
In the vasculature, PI3Kδ is expressed by endothelial cells and participates in neutrophil trafficking by modulating the proadhesive state of these cells in response to TNFalpha (Puri et al. Blood (2004) 103(9) p. 3448-56.). A role for PI3Kδ in TNFalpha-induced signalling of endothelial cells is demonstrated by the pharmacological inhibition of Akt phosphorylation and PDK1 activity. In addition, PI3Kδ is implicated in vascular permeability and airway tissue edema through the VEGF pathway (Lee et al. J. Allergy Clin. Immunol. (2006) 118(2) p. 403-9). These observations suggest additional benefits of PI3Kδ inhibition in asthma by the combined reduction of leukocyte extravasation and vascular permeability associated with asthma. In addition, PI3Kδ activity is required for mast cell function both in vitro and in vivo (Ali et al. Nature (2004) 431 p. 1007-11; and Ali et al. J. Immunol. (2008) 180(4) p. 2538-44) further suggesting that PI3K inhibition should be of therapeutical benefit for allergic indications such asthma, allergic rhinitis and atopic dermatitis.
The role of PI3Kδ in B cell proliferation, antibody secretion, B-cell antigen and IL-4 receptor signalling, B-cell antigen presenting function is also well established Okkenhaug et al. (2002), above; Al-Alwan et al. J. Immunol. (2007) 178(4) p. 2328-35; and Bilancio et al. Blood (2006) 107(2) p. 642-50) and indicates a role in autoimmune diseases such as rheumatoid arthritis or systemic lupus erythematosus (SLE). Therefore PI3K inhibitors may also be of benefit for these indications.
Pharmacological inhibition of PI3Kδ inhibits fMLP-dependent neutrophil chemotaxis on an ICAM coated agarose matrix integrin-dependent biased system (Sadhu et al., J. Immunol. (2003) 170(5) p. 2647-54.). Inhibition of PI3Kδ regulates neutrophil activation, adhesion and migration without affecting neutrophil mediated phagocytosis and bactericidal activity over Staphylococcus aureus (Sadhu et al. Biochem. Biophys. Res. Commun. (2003) 308(4) p. 764-9). Overall, the data suggest that PI3Kδ inhibition should not globally inhibit neutrophil functions required for innate immune defence. PI3Kδ's role in neutrophils offers further scope for treating inflammatory diseases involving tissue remodeling such as COPD or rheumatoid arthritis.
PI3Kδ inhibition may also lead to cancer immunotherapy. For instance, PI3Kδ has a critical signalling role in regulatory T cells (Tregs), which enables their expansion (Patton et al. PLoS One. 2011; 6(3):e17359). Activation of Tregs is one of the key processes that allow cancer cells to build immunological tolerance and escape immune surveillance. Another aspect of cancer immunity where PI3Kδ inhibitors may play a role is in upregulating the expression of PD-L1 (Programmed cell death 1 ligand 1) as has been shown in cultured airway epithelial cells (Kan-O et al. Biochem Biophys Res Commun. 2013; 435(2):195-201). PD-L1, expressed on various cell types such as T and B lymphocytes, NK and DC cells or epithelial cells, is involved in suppressing T cell dependent immunity such as the activation of cytotoxic CD8 T cells. Neutralising antibodies targeting PD-L1 are currently being developed as cancer immuno-therapeutics. Therefore, PI3Kδ inhibition may provide a novel way of enhancing anti-tumour responses. A similar rationale may also be applied to anti-infective immunity where the balance of Tregs and CD8s are known to play an important role in the outcome of the immune response such as viral infections.
The central nervous system (CNS) is also enriched with PI3Kδ expression (Eickholt et al. PLoS One 2007 11; 2(9):e869). A more recent report further uncovered a link between PI3Kδ and the neuregulin NRG-1 and ErbB4 receptor in the CNS with implications for schizophrenia (Law et al. Proc Natl Acad Sci USA. 2012; 109(30):12165-70). It was previously known that increased expression of a splice variant of ErbB4 containing the cytoplasmic portion, Cyt1, resulted in activation of the PI3K pathway as well as increased risk of schizophrenia. The publication by Law et al. indicates that the schizophrenia genetically associated Cyt1 couples preferentially to the PI3Kδ isoform. Furthermore, the PI3Kδ selective inhibitor, IC87114, showed remarkable efficacy in a mouse model of amphetamine-induced psychosis (Law et al. Proc Natl Acad Sci USA. 2012; 109(30):12165-70). Therefore PI3Kδ inhibitors have the potential to form the basis for new schizophrenia therapy approaches.
In addition, there is also good evidence that class IA PI3K enzymes also contribute to tumourigenesis in a wide variety of human cancers, either directly or indirectly (Vivanco and Sawyers, Nature Reviews Cancer (2002) 2(7) p. 489-501). For example, inhibition of PI3Kδ may have a therapeutic role for the treatment of malignant haematological disorders such as acute myeloid leukaemia (Billottet et al. Oncogene (2006) 25(50) p. 6648-59). Moreover, activating mutations within p110α (PIK3CA gene) have been associated with various other tumours such as those of the colon and of the breast and lung (Samuels et al. Science (2004) 304(5670) p. 554).
It has also been shown that PI3K is involved in the establishment of central sensitization in painful inflammatory conditions (Pezet et al. The J. of Neuroscience (2008) 28 (16) p. 4261-4270).
A wide variety of retroviruses and DNA based viruses activate the PI3K pathway as a way of preventing host cell death during viral infection and ultimately exploiting the host cell synthesis machinery for its replication (Virology 344(1) p. 131-8 (2006) by Vogt et al.; and Nat. Rev. Microbiol. 6(4) p. 265-75 (2008) by Buchkovich et al.). Therefore PI3K inhibitors may have anti-viral properties in addition to more established oncolytic and anti-inflammatory indications. These antiviral effects raise interesting prospects in viral induced inflammatory exacerbations. For example, the common cold human rhinovirus (HRV) is responsible for more than 50% of respiratory tract infections but complications of these infections can be significant in certain populations. This is particularly the case in respiratory diseases such as asthma or chronic obstruction pulmonary disease (COPD). Rhinoviral infection of epithelial cells leads to a PI3K dependent cytokine and chemokine secretion (J. Biol. Chem. (2005) 280(44) p. 36952 by Newcomb et al.). This inflammatory response correlates with worsening of respiratory symptoms during infection. Therefore PI3K inhibitors may dampen an exaggerated immune response to an otherwise benign virus. The majority of HRV strains infect bronchial epithelial cells by initially binding to the ICAM-1 receptor. The HRV-ICAM-1 complex is then further internalised by endocytosis and it has been shown that this event requires PI3K activity (J. Immunol. (2008) 180(2) p. 870-880 by Lau et al.). Therefore, PI3K inhibitors may also block viral infections by inhibiting viral entry into host cells.
PI3K inhibitors may be useful in reducing other types of respiratory infections including the fungal infection aspergillosis (Mucosal Immunol. (2010) 3(2) p. 193-205 by Bonifazi et al.). In addition, PI3Kδ deficient mice are more resistant towards infections by the protozoan parasite Leishmania major (J. Immunol. (2009) 183(3) p. 1921-1933 by Liu et al.) or by the intracellular bacteria Listeria (Pearce et al. J. Immunol. (2015) 195(7) p. 3206-17). Taken with effects on viral infections, these reports suggest that PI3K inhibitors may be useful for the treatment of a wide variety of infections.
A published report points towards PI3Kδ inhibitors having potential benefits in preventing infections by the common airway bacterial pathogen S. Pneumoniae (Fallah et al., Mech. Ageing Dev. 2011; 132(6-7): 274-86). In this report PI3Kδ is shown to reduce the macrophage-derived cytokines required to mount an effective antibody response to S. pneumoniae in the elderly. The anti-bacterial benefit of PI3Kδ inhibitors may thus be useful in the treatment of bacterial respiratory tract infections and bacterial exacerbations of respiratory conditions and lung damage such as asthma, COPD and cystic fibrosis, and pneumonia.
PI3K inhibition has also been shown to promote regulatory T cell differentiation (Proc. Natl. Acad. Sci. USA (2008) 105(22) p. 7797-7802 by Sauer et al.) suggesting that PI3K inhibitors may serve therapeutic purposes in auto-immune or allergic indications by inducing immuno-tolerance towards self antigen or allergen. The PI3Kδ isoform has also been linked to smoke induced glucocorticoid insensitivity (Am. J. Respir. Crit. Care Med. (2009) 179(7) p. 542-548 by Marwick et al.). This observation suggests that COPD patients, which otherwise respond poorly to corticosteroids, may benefit from the combination of a PI3K inhibitor with a corticosteroid.
PI3K has also been involved in other respiratory conditions such as idiopathic pulmonary fibrosis (IPF). IPF is a fibrotic disease with progressive decline of lung function and increased mortality due to respiratory failure. In IPF, circulating fibrocytes are directed to the lung via the chemokine receptor CXCR4. PI3K is required for both signalling and expression of CXCR4 (Int. J. Biochem. and Cell Biol. (2009) 41 p. 1708-1718 by Mehrad et al.). Therefore, by reducing CXCR4 expression and blocking its effector function, a PI3K inhibitor should inhibit the recruitment of fibrocytes to the lung and consequently slow down the fibrotic process underlying IPF, a disease with high unmet need.
Attempts have been made to prepare compounds which inhibit PI3-kinase activity and a number of such compounds have been disclosed in the art. However, in view of the number of pathological responses which are mediated by PI3-kinases, there remains a continuing need for inhibitors of PI3-kinase which can be used in the treatment of a variety of conditions.
The present inventors have discovered compounds which are inhibitors of kinase activity, in particular PI3-kinase activity. Compounds which are PI3-kinase inhibitors may be useful in the treatment of disorders associated with inappropriate kinase activity, in particular inappropriate PI3-kinase activity, for example in the treatment and prevention of disorders mediated by PI3-kinase mechanisms. Such disorders include respiratory diseases including asthma, chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF); ciliopathy including primary ciliary dyskinesia, polycystic liver disease and nephronophthisis; bacterial infections including bacterial respiratory tract infections, for example infections by S. Pneumoniae, H. Influenzae, M. Catarrhalis and/or mycobacteria such as Mycobacterium tuberculosis, and bacterial exacerbations of respiratory conditions and lung damage such as asthma, COPD and cystic fibrosis; viral infections including viral respiratory tract infections, for example infections by influenza, rhinovirus, respiratory syncytial virus (RSV), human parainfluenza virus (HPIV), adenovirus and/or coronavirus, and viral exacerbation of respiratory conditions and lung damage such as asthma, COPD and cystic fibrosis; other non-viral respiratory infections including aspergillosis and leishmaniasis; allergic diseases including allergic rhinitis, atopic dermatitis and psoriasis; autoimmune diseases including ankylosing spondylitis, Churg-Strauss syndrome, Crohn's disease, Glomerulonephritis, Henoch-Schonlein purpura, idiopathic thrombocytopenic purpura (ITP), interstitial cystitis, pemphigus, primary sclerosing cholangitis, psoriasis, rheumatoid arthritis, sarcoidosis, Sjogren's syndrome, Type 1 diabetes, ulcerative colitis, vasculitis and Wegener's granulomatosis; inflammatory disorders including inflammatory bowel disease; diabetes; cardiovascular diseases including thrombosis, atherosclerosis and hypertension; hematologic malignancies; neurodegenerative diseases; pancreatitis; multiorgan failure; kidney diseases; platelet aggregation; cancer; sperm motility; transplantation rejection; graft rejection; lung injuries; pain including pain associated with rheumatoid arthritis or osteoarthritis, back pain, general inflammatory pain, post hepatic neuralgia, diabetic neuropathy, inflammatory neuropathic pain (trauma), trigeminal neuralgia and Central pain; fibrotic diseases; depression; and psychotic disorders including schizophrenia.
In one embodiment, compounds of the invention may show selectivity for PI3-kinases over other kinases.
In another embodiment, compounds of the invention may be potent inhibitors of PI3Kδ.
In another embodiment, compounds of the invention may show selectivity for PI3Kδ over other PI3-kinases.
In a further embodiment, compounds of the invention may have properties which make them particularly suitable for oral administration.